Apparatus for depositing diamond and refractory materials comprising rotating antenna

ABSTRACT

An improved plasma enhanced chemical vapor deposition (CVD) reactor is provided for the synthesis of diamond and other high temperature materials such as boron nitride, boron carbide and ceramics containing oxides, nitrides, carbides and borides, or the like. An aspect of the present method enables a plasma to substrate distance to be optimized for a given surface. This has been found to enable a substantially uniform thin film coating or diamond or lake material to be deposited over a substrate.

BACKGROUND

The field of the present invention relates generally to a plasmaenhanced chemical vapor deposition (CVD) reactor. In particular, thefield of the present invention relates to a plasma CVD device suitablefor the synthesis of materials such as diamond, boron nitride, boroncarbide, ceramics containing oxides, nitrides, carbides and borides, orthe like, and for the deposition of a uniform thin film layer of galliumnitride, or the like, over a substrate.

Diamond and other high temperature materials such as boron nitride,boron carbide, and ceramics containing oxides, nitrides, carbides andborides are finding increasing uses because of their high temperatureand wear resistance, and high strength. In particular, there isincreasing demand for coatings of these materials to be deposited onordinary materials to impart wear resistance, abrasion resistance, andhigh temperature resistance.

A conventional plasma enhanced CVD reactor employs microwaves to producea stable plasma. The apparatus consists of a microwave generator, atuning element, a waveguide, and a quartz tube. The quartz tube ispassed through the waveguide, and a substrate is placed inside thequartz tube in the region where it passes through the waveguide.Suitable gases are introduced into the tube, for example in the case ofdiamond synthesis, a mixture of methane and hydrogen. The plasma isformed inside the tube by the microwave radiation, and a diamond layeris deposited on the substrate surface. The substrate size is limited tovery small sizes by the physical dimensions of the microwave cavity.

A second conventional technique also employs microwaves to producestable plasmas. The apparatus consists of a microwave cavity, a vacuumchamber connected to the microwave cavity by means of a microwavetransparent window, and a microwave generator and waveguide to introducemicrowaves into the microwave cavity. A magnetic field is generated bymagnets external to the microwave cavity. The magnets have a polarityand magnitude suitable to create an electron cyclotron resonance (ECR)condition within the chamber. This technique has a disadvantage in thatthe pressure of the gas is limited to 0.5 torr or less by the necessityof maintaining the electron cyclotron resonance condition. Accordingly,the deposition rates of diamond materials are very low.

A third type of conventional plasma reactor also employs microwaves toproduce stable plasmas. The type of plasma reactor is represented byU.S. Pat. No. 4,940,015. The apparatus consists of a microwave cavity, avacuum chamber connected to the microwave cavity by means of a microwavetransparent window, and a microwave generator and waveguide to introducemicrowaves into the microwave cavity. The chamber is of suitabledimensions so as to create a cavity resonance condition for theefficient absorption of microwave energy by the plasma. However, it isnot possible to move the plasma relative to the substrate surface, andhence the substrate size is limited.

Conventional methods of coupling an E field into a microwave cavity suchas is shown in U.S. Pat. No. 4,866,346 employ a mode coupler. See forexample, the '346 patent at col. 7, lines 42-43. A conductive rod passesfrom an input waveguide into a cylindrical cavity, characterized as anoutput waveguide. The conductive rod passing between the waveguides is amode coupler. This configuration has the disadvantage of limitingsubstrate size. Also, the mode coupler exhibits inferior plasmastability. Consequently, the plasma cannot be closely controlled to forma uniform coating of a diamond or refractory material.

As will be explained, the present invention uses an antenna radiator,rather than a microwave coupler, for radiating an E field of maximizedintensity into a stable microwave cavity. This provides an E field ofmaximized intensity which produces a plasma that can be closelycontrolled to precise tolerances.

It is not possible with conventional plasma enhanced CVD reactors tocontrol the plasma to the degree necessary for certain new semiconductorprocessing applications such as, for example, deposition of diamondfilms. It would be advantageous to grow single crystal thin filmdiamonds in a CVD process for electronic applications. The presentlyknown conventional plasma enhanced CVD techniques described above areunable to produce single crystal diamond films which are large enoughfor electronic devices.

Single-crystal thin film diamonds promise broad utility in electronicapplications. Diamond materials for electronics consist of a singlecrystal structure and contain doping materials to make themsemiconductive.

A diamond material is unique in that it has higher thermal conductivitythan any other material at room temperature and above. Thus, diamondcircuits could be more stable than conventional semiconductor circuitsand remove accumulated heat faster. Another advantageous property ofdiamond is its large energy band gap, 5.45 electron volts, as comparedto only 1.1 electron volts for silicon.

The large band gap of a diamond would enable it to operate at extremelyhigh voltages and at high currents. Diamond electronic devices also canoperate at high frequencies. A diamond device could run at speeds of 300GHz as opposed to 10 MHz for the device that currently powers the IBMPC-AT.

The foregoing properties enable electronic devices made with diamond towork faster, withstand more power and fit closer together than currentdevices. This would also mean that electronic circuits based upondiamond materials could form the basis for extremely high-speedcomputing devices. Because diamond is harder and more durable than anyother semiconducting material, diamond circuits will resist harshenvironments that would melt or corrode existing semiconductors.

The use of diamonds in electronics is currently limited by the inabilityof conventional plasma enhanced CVD devices to produce uniform, thinfilm diamond coatings in sufficient quantity over a large enough area tomake a diamond based electronic device commercially practical.

Conventional plasma enhanced CVD devices have limitations in producingdiamond coatings which arise from their inability to precisely controlthe plasma with respect to the substrate being coated. The nature of theplasma depends upon many independent variables such as electronconcentration, electron-energy distribution, gas density and so forth.It has not been possible with conventional plasma enhanced CVD devicesto control these variables to a sufficient degree to produce a singlecrystal diamond coating over a large wafer in commercially feasiblequantities. Conventional devices also lack the ability to control theplasma to the extent necessary to produce single-crystal diamond filmswith sufficient uniformity to be used in commercial quantities.

Another major drawback of current CVD deposition techniques is therequirement for abrasive treatment of substrate surfaces prior todeposition to promote nucleation and growth of continuouspolycrystalline diamond layers. Although bias enhanced nucleation hasbeen attempted, it is not apparent that this technique can be applied tonon-conducting substrates.

Therefore, what is needed is an improved plasma enhanced CVD apparatuswhich is capable of optimizing the plasma to substrate contact to thedegree necessary to provide diamond synthesis in commercial quantities.

What is also needed is an improved plasma enhanced CVD reactor capableof producing single crystal thin film diamond with requisite uniformityand in wafers large enough to be commercially practicable for electronicdevices.

It would also be advantageous to provide an improved plasma enhanced CVDreactor capable of rapid thermal processing for producing largequantities of uniform thin film coatings of materials such as galliumnitride or the like over substrates at a greater rate than waspreviously possible.

What is also needed is a method for forming a diamond coating or thelike which contains as an integral step within the same system, aprocess for forming a nucleation layer on which the diamond will grow byitself. What is also needed is a process for forming a nucleation layer,integral with a system for forming a diamond coating, wherein theprocess for forming a nucleation layer does not rely on the use ofsubstrate bias and is applicable to non-conducting substrates, as wellas to conducting substrates.

It would also be advantageous to incorporate the process for forming anucleation layer integrally with the same system for creating a diamondlayer in order to further enhance diamond growth and to eliminate theneed for providing two separate systems, one for creating a nucleationlayer, as a base for diamond growth, and another system for depositingthe diamond coating.

SUMMARY

In order to overcome the above-discussed disadvantages of known plasmaenhanced CVD reactors, one aspect of the present invention providesplasma CVD reactor which has a coupling antenna rotatable about adesired axis of rotation with at least two degrees of freedom to directthe stable plasma to move about the substrate surface over a larger areaand with greater controllability than was previously possible. Thisenables the diameter of a diamond deposition to be approximately equalto the plasma diameter for each point to which the plasma is directed asthe plasma is moved across the target substrate. A means are providedfor swiveling the coupling antenna about an axis of rotation so that itmoves with at least two degrees of freedom with respect to a targetsurface. The antenna can also be pivoted as well as swiveled in order tomake the plasma ball scan the surface of any substrate to be coated.Accordingly, this aspect of the present invention is capable ofproducing a coating which is of uniform thickness over a greater area ofsubstrate surface than was previously possible.

A device according to one aspect of the present invention is capable ofproviding a uniform thin film deposition of diamond or other materialwhich is equal approximately to the locus of points defining an optimalplasma to substrate contact as the plasma is moved over the substrate. Aplasma enhanced CVD reactor according to this aspect of the presentinvention is capable of producing a wafer or coating having a closelycontrolled uniform thickness at least 4 inches (10 centimeters) indiameter. This produces a wafer of approximately 75 cm². Previously, itwas possible to produce a diamond wafer or coating having a uniformthickness over an area of only about 1.5 cm in diameter. Thus, a plasmaenhanced CVD reactor incorporating the present invention is able toproduce a diamond coating of uniform thickness over fifty times the areathat was possible in the prior art.

For example, U.S. Pat. No. 4,940,015, at column 7, line 48 and column 8,line 14, teaches that a diamond film of 3 inches in diameter may beformed on the surface of the silicon substrate. However, the coatingperformed by U.S. Pat. No. 4,940,015 is not uniform. Thus, the coatingmust be subjected to further expensive processing steps in order toprovide a uniform thickness to make a functional electronic device. Alayer exhibiting a nonuniform, uncontrolled thickness is useless forsemiconductor applications.

According to one aspect of the present invention, the coupling antennais movable in at least two degrees of freedom. Therefore, the antenna iscapable of bringing the plasma ball in a highly controlled, intimatecontact with the substrate surface. It will be appreciated that anotheraspect of the present invention provides a means for optimizing theplasma to substrate distance over all portions of a substrate. This alsoenables a material such as diamond to be grown uniformly over a greaterarea than was previously possible. Means are provided for adjusting theangle of rotation of the antenna automatically to optimize the plasma tosubstrate distance over a locus of points defining the entire substratesurface to be coated. Note that this optimization of plasma to substratedistance is capable of providing a diamond coating of a uniformthickness over any type of substrate.

The substrate is not limited to a planar surface as in conventionaltechniques. Means are also provided for moving the substrate holder upor down with respect to the antenna, thereby further increasing controlof the plasma over a larger scanable area of a substrate surface. It hasbeen found that the substrate holder can be moved in a verticaldirection with respect to the antenna without disturbing the resonanceof the microwave cavity. This aspect of the present invention has theadvantage of greatly increasing the coating rate of a diamond film whileat the same time expanding the area coated with a uniform coating toover fifty times that of known techniques.

In accordance with another aspect of the present invention, the base ofthe plasma chamber consists of a water-cooled window comprising amaterial such as quartz which is transparent to visible light. Thisenables a lamp array disposed beneath the plasma chamber to irradiateand to heat up a target substrate from beneath. The use of the lamp toheat the bottom surface of the substrate may be used to create anucleation layer which facilitates diamond growth on the top of thesubstrate. For example, silicon carbide can be deposited by plasmaenhanced CVD on the top of a substrate heated by the lamp array. Theheated silicon carbide forms a nucleation layer which enhances thegrowth of the diamond layer to be deposited on top of the siliconcarbide layer. The use of the lamp array to irradiate the substrate frombeneath increases the rate of thermal processing and has the advantageof enabling additional layers to be deposited by the plasma on the topsurface of the substrate in a shorter time than was previously possible.

The inclusion of the lamp array for heating the substrate has anadditional advantage over conventional plasma enhanced CVD devices inthat it eliminates electrical interference with the plasma. Inconventional plasma enhanced CVD reactors, the back side or underneathsurface of the substrate or wafer is heated by an inductive heatingprocess. This has the disadvantage that the power supply for theinductive heating must be carefully isolated from the substrate in orderto eliminate any electrical interference which could adversely affectthe plasma. Also, conventional CVD reactors incorporating inductiveheating must be carefully shielded or must incorporate additionalfeatures to screen the substrate from electrical interference. This addsconsiderably to the cost of such a reactor.

A further advantage of this aspect of the invention is that the lamparray enables a nucleation layer to be provided nonabrasively on asubstrate in the same system for creating a diamond coating. Theformation of the nucleation layer is thus fully integrated in the samesystem for creating the diamond coating. This completely eliminates theneed for two separate systems, one for creating the nucleation layer andanother system for creating the diamond coating. This also achieves atremendous savings in cost by eliminating an entire system for creatinga nucleation layer and also greatly facilitates the time needed tocreate a diamond coating.

As a further advantage of this aspect of the invention, the nucleationlayers are created without the need for applying a bias to a substrateand thus, this aspect of the invention can be employed for creating anucleation layer on nonconductive substrates.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other advantages of the present invention may be appreciatedfrom studying the following detailed description of the presentlypreferred exemplary embodiment together with the drawings in which:

FIG. 1 is an overall side view of a first embodiment according to thepresent invention;

FIG. 2 is an enlarged side view of the embodiment depicted in FIG. 1.

FIG. 3 is a chart showing process conditions for producing differenttypes of diamond coating using the present invention.

FIG. 4 shows an electric field pattern inside a rectangular waveguidewhich is coupled by a swiveling antenna into a process chamber inaccordance with one aspect of the present invention.

FIG. 5 shows an alternate embodiment of the present inventionincorporating a plurality of antennas.

DETAILED DESCRIPTION

Referring to FIG. 1, the apparatus according to one aspect of thepresent invention provides an improved plasma enhanced CVD apparatuswhereby layers of diamond, boron nitride, boron carbide, and ceramicscontaining oxides, nitrides, carbides and borides, as well as epitaxialfilms for semiconductor device applications, such as gallium nitride, orthe like, can be deposited with closely controlled, uniformed thicknesson suitable surfaces using a high pressure microwave plasma.

A microwave generator 100 is provided for creating radio frequency inthe microwave region. The microwave generator 100 is typically amagnetron with an output power of approximately 6-30 kW. This generatesmicrowaves in a range of 0.8-3 GHz and above. This is the acceptedindustry standard for plasma enhanced CVD processing. The microwavegenerator 100 is operatively connected to the circulator 102. Thecirculator 102 is a commercially available circulator such as made byPhilips Corporation. Circulator 102 comprises a conventional means forphase shifting the reflected radiation which is reflected back towardthe microwave generator through the non-impedance matched load.

The circulator 102 is connected to a rectangular waveguide 104. Therectangular waveguide 104 receives microwaves from the circulator 102. Athree stub tuner 108 comprises three metallic cores which canselectively impinge into the rectangular waveguide 104. The metal coresof the three stub tuner 108 are adjustable to selectively place acomplex reactance into the rectangular waveguide 104. Thus, the threestub tuner 108 provides a means for impedance matching the microwavefrequency into the load. This allows precise impedance matching of theload to the source. Once the three Stub tuner has been adjusted toimpedance match into the load, it can be locked in a particularconfiguration to provide a constant impedance matching function.

The rectangular waveguide 104 is further provided with a sliding short110 which makes electrical contact to the interior of the waveguide 104.The sliding short 110 is provided with an adjusting arm 112. Inaccordance with known techniques, the distance between the sliding short110 and antenna 106 can be lengthened or shortened in order to vary thewavelength of the microwave energy traveling through the waveguide. Thesliding short 110 moves in a horizontal direction as shown by the arrowsin FIG. 1. A microprocessor (not shown) adjusts the sliding short 110 inaccordance with well-known techniques in order to optimize thewavelength for the substance being coated in the process chamber 114.

The three stub tuner 108 comprises a plurality of plungers and issimilar in function to an E-H tuner. A metal core is inserted into eachplunger and can be selectively inserted into the waveguide at variouspositions. This enables the reflection power to the power source to bereduced by matching the source impedance to the entire load impedance.

A process chamber 114 is constructed of a suitable material such asstainless steel and is arranged in a cylindrical or rectangular shape.The process chamber 114 includes means for cooling the chamber surfaces.For example, the process chamber 114 in a preferred embodiment is ofdouble walled construction. The cavity 116 is preferably filled withwater or other coolant to provide efficient cooling of the processchamber.

A quartz ring support fixture 118 is attached to a motor driven stage120. The quartz ring support fixture 118 is introduced into the processchamber 114 through one of the chamber sides. A metallic rod 122preferably made of molybdenum, passes through the quartz ring supportfixture 118 to make an ohmic contact to a metal substrate holder 124.The substrate holder 124 is disposed on the quartz ring support fixture118. The metallic rod 122 is connected through a vacuum seal 126 to anexternal HF, RF, or DC power supply. The metallic rod 122 also providesmeans for rotating substrate holder 124 by actuator 190. The powersupply provides a positive or negative bias to the substrate holderwhich can selectively vary the intensity of electron or ion bombardmentin accordance with well-known techniques.

In a preferred embodiment, a 13.56 MHz RF power supply providessubstrate bias or potential enhancement of diamond nucleation. The RFpower supply has been found to be useful as means for providing initialnucleation with faster growth rate and uniformity. In addition, the RFpower supply also provides a convenient means for microwave plasmaignition. It has been found that a plasma easily can be ignited with themicrowave power under 200 W. The quartz ring support 118 passes throughmetallic bellows 128. The metallic bellows 128 also provide means forselectively varying the position of the quartz ring support fixture 118within the process chamber 114. The metallic bellows 128 in conjunctionwith springs 129 also provide means for centering and leveling thesubstrate holder in the plasma chamber. Micrometer screws 130 aid inprecisely positioning the substrate holder.

A rectangular gate valve is fixed to one side 10 of the process chamber114 for the purpose of introducing and withdrawing substrates andsubstrate holders from the process chamber in a well-known manner. Othersides of the process chamber 114 are used to introduce gases into thechamber and to affix various pressure gauges, site ports, and otherinstruments in accordance with techniques which are well-known. Theprocess chamber access ports, also located on the process chamber sides,permit plasma diagnostics and in-situ surface analysis to be performed.In a preferred embodiment, the system is fully automated, utilizing amicroprocessor to provide process control, data process collection,analysis and display. Once the substrate is loaded, the system providescomplete control in real time process including gas, vacuum, pressure,plasma formation, temperature and substrate position. The motorizedwafer stage is also microprocessor controlled in accordance withtechniques which are well-known and is used to position automaticallythe substrate.

The base of the process chamber 114 is sealed by a quartz window 133comprising two substantially adjacent quartz plates 134a, 134b. Thewindow 133 may be fabricated from any material which is transparent tovisible light. The preferred material is quartz. The quartz plates 134a,134b are separated by an interstitial space 135 which is cooled by wateror other coolant material circulating therein from a coolant reservoir136.

The interstitial spaces 135 are optimized to maximize the transmissionof lamp radiation and to maximize heat transfer to the coolant. Thepractical limit for the interstitial space 135 is greater than 0.001 in.and less than 0.010 in.

A conventional pumping means 137 circulates coolant throughout theinterstitial space 135. The interstitial space 135 of an optimal widthto accommodate a fluid flow rate which prevents the formation of thermaldiscontinuities or hot spots on the quartz plates 134a, 134b. Thisfacilitates the heating of the substrate 142 to a greater degree thanwas previously possible and increases the rate of growth of a nucleationlayer on the substrate.

In a conventional plasma CVD process, the nucleation layer must beformed in a separate system, created specifically for that purpose.Typically, the substrate is abrasively treated, such as by abrading withdiamond paste and sandpaper, to promote nucleation as a foundation forthe growth of a continuous polycrystalline diamond layer, or the like.This disadvantageously increases processing costs and the time forforming the diamond layer. Also, the formation of the diamond layer isrestricted to those areas of the substrate where the nucleation layerhas been adequately formed.

It will be appreciated that, in accordance with this aspect of thepresent invention, the process for creating a nucleation layer on thesubstrate is integrated into the same system and is integral with theprocess for forming the diamond coating over the substrate.

In accordance with this aspect of the invention, a tungsten-halogen lamparray 138 is disposed beneath the quartz window 133 and is used touniformly radiantly heat the substrate and the substrate holder 124.

This aspect of the invention contemplates the use of any material forthe window. The important factor is that the window is transparent to asource of synergistic stimulation having a predetermined wavelength forforming a nucleation layer on the surface of the substrate. In apreferred embodiment the source of synergistic stimulation is a lamparray 138.

Window 133 enables the lamp array 138 to advantageously heat thesubstrate from beneath at the same time that the plasma is impingingupon the target substrate from above. The transparent window 133 incombination with the lamp array 138 provide a means for facilitating thecreation of a nucleation layer on the target substrate. Epitaxial,polycrystalline, and amorphous growth of a substance such as diamond canthen occur at a much faster rate on top of the nucleation layer. Anucleation layer can be made by chemical vapor deposition on top of thetarget substrate by such materials as, for example, boron carbide,silicon carbide, aluminum nitrite, aluminum carbide, germanium carbide,and others. The nucleation layer is quickly grown due to the irradiationof the target substrate by the lamp array 138 through the transparentwindow 133. The easily created nucleation layer has been found toenhance the growth of a diamond layer which is then deposited on top ofthe nucleation layer.

It will be appreciated that this aspect of the invention, in combinationwith other features of the invention described herein, makes possibleepitaxial growth of a diamond layer on the substrate, as well aspolycrystalline or amorphous growth of a diamond layer. Epitaxial,polycrystalline or amorphous growth of other substances forsemiconductor device applications are also possible using the presentinvention.

FIG. 3 shows a summary of process conditions for various types of adiamond coating produced in accordance with the present invention. Forexample, polycrystalline diamond layers, nanocrystalline diamond anddiamond like carbon (DLC) are shown.

In accordance with one aspect of the present invention, apolycrystalline diamond layer can be deposited on an untreated siliconsurface by first depositing a nanocrystalline diamond layer. This methoddoes not rely on the use of a substrate bias and therefore is believedapplicable to nonconducting substrates.

A turbomolecular pump was used to evacuate the process chamber to atypical base pressure of 1×10⁻⁶ torr prior to each deposition run.Processes B and C can be used to deposit films on untreated polishedsilicon wafers. Process B followed by Process A results in thedeposition of continuous polycrystalline diamond layers without anysubstrate preparation. Deposition conditions for process B are similarto those used to deposit polycrystalline diamond films (process A), withthe exception that in process B the substrate surface is more distantfrom the plasma ball, resulting in less heating of the substrate by theplasma.

The use of the lamp array 138 to irradiate the target substrate frombelow is also advantageous because it has been found to be an extremelyefficient way to heat the target substrate. Also, the irradiation of thetarget substrate by a lamp array 138 eliminates electrical interferencewhich is often found in conventional methods employing inductive heatingof the substrate. In conventional plasma enhanced CVD devices, powersupplies must be carefully isolated from a substrate heated throughinductive heating methods in order to prevent electrical interferenceand consequent irregularities in the formation of the epitaxial coating.

The detail of the upper portion of the process chamber including theantenna is described with reference to FIG. 2. The inner wall 140 ofprocess chamber 114 forms a circular resonant cavity with the substrateholder 124. A substrate 142 is disposed upon the substrate holder 124for contact with a plasma ball 144. In a preferred embodiment, thesubstrate holder 124 is moveable up and down in a vertical direction.The substrate holder 124 is preferably insulated and is connected with acomputer driven stage to vary the distance from the plasma to thesubstrate as will be explained.

The upper portion of the process chamber 114 comprises a removablestructure 150 suitably arranged to allow microwave radiation in thewaveguide 104 to pass into the process chamber 114. The waveguide 104 iscoupled to a window 154 which is constructed of a suitablemicrowave-transparent material such as quartz.

In accordance with one aspect of the present invention, antenna 106comprises an antenna radiator rather than a conventional microwavecoupler. The use of antenna radiator 106 provides a means for radiatingan E field of maximized intensity at a transmitting end. Thisconsequently also provides a means for optimal control of a plasma ball144 such that the high intensity plasma ball 144 can be preciselydirected to any point on a substrate with greater control and precisionthan was previously possible with conventional mode coupler devices.

It has been found that the strength of the E field associated withmicrowave radiation in the waveguide 104 is maximized in the center ofwaveguide 104. Since the wall is a conductor, the field at the wall iszero. In accordance with this aspect of the invention, an antenna 106has a first receiving end disposed substantially in the center ofwaveguide 104 and transversely to the longitudinal axis of the waveguide104. The E field is oscillated in the conductive waveguide 104 byadjusting three stub tuner 108 in accordance with known techniques suchthat it attains a frequency characterized by maximized propagation andintensity for a desired mode, for example a TE₁₀ mode. The E field thenoscillates in the antenna 106. A transmitting end of antenna 106 isprovided as a means for radiating the E field with maximized intensityinto the process chamber 114.

Antenna 106 is disposed generally orthogonally within waveguide 104 andpasses into the chamber defined by quartz window 154. It will beappreciated that quartz window 154 and antenna 106 both extend into theprocess chamber 114. In a preferred embodiment, antenna 106 is=disposedbelow the level of the upper inner wall 104 of the process chamber 114.Antenna 106 thus directs the maximum E field from the waveguide 104 sothat a plasma forms above the substrate holder 124 which is attached tothe movable quartz ring support fixture 118.

In accordance with the foregoing aspect of the invention, a TE₁₀ mode istransmitted from microwave generator 100 into rectangular waveguide 104.The electric field pattern inside waveguide 104 is shown in FIG. 4.

The antenna 106 couples the maximum oscillating E field inside waveguide104 into a circular waveguide 111. The oscillating E field is radiatedfrom the end of antenna 106 into the resonant cavity formed by thechamber walls 140 and the substrate platen 124.

The maximum E field inside the resonant cavity is actually a distanceaway from the window 154. Therefore, the plasma 144 does not contact thewindow 154. Furthermore, it has been found that the maximum E field willfollow the vector pointing from the antenna. Therefore, the plasma 144will follow the direction of the antenna 106 when the antenna 106 isswivelled about an axis of rotation formed by the ball joint 182 andsocket member 184. Alternatively, it will be appreciated that the balljoint 182 and socket member 184 form an axis of rotation or pivot axis.The coupling antenna 106 is then swingably moveable about the axis ofrotation to direct the stable plasma 144 to move about the substratesurface. Also, antenna 106 may be simultaneously moved up and down in avertical axis with respect to the substrate. This arrangement provides acoupling antenna 106 swingably moveable about an axis of rotation withat least two degrees of freedom which directs a stable plasma 144 tomove as directed at an optional point of contact about the substratesurface.

In accordance with another aspect of the invention, quartz window 154behaves as a dielectric reflector. The dielectric reflector comprises anintegral part of the microwave circuit and has been found to greatlyinfluence the radiation of the microwave energy into the processchamber. In this regard, the position of tuning elements 108 and 112 areset to cancel reflected microwave power caused by dielectric reflector154. This enables the dielectric reflector to closely control and tomaximize the electric vector of the radiated microwave energy. Thedielectric reflective properties of quartz window 154 have been found toprovide a means for generating stability in the plasma ball 144.

The antenna 106 and quartz window 154 are cooled by forced air as shownby arrow 160. In a preferred embodiment, a cooling passage is providedthough the core of antenna 106 along its longitudinal axis for theinfusion of compressed air. Compressed air cools the inside of antenna106 and is also directed against the quartz window 154 as shown by thearrows.

The process of igniting the gases to form the plasma is well-known.Generally, the microwave power from the antenna 106 is transferred toelectrons and the gas is ignited producing a plasma in the regionexisting all over the cross-section of the process chamber 114. At theoptimum gas pressure range, a dense plasma is produced locally near thesubstrate surface and located distant from the quartz window 154. Inaccordance with the present invention, it has been found that thedirection and location of the plasma ball can be closely controlled bypivoting or swiveling the coupling antenna about a desired axis ofrotation. Also, it has been found that the substrate holder can be movedin a Z axis or vertical direction without disturbing the resonance ofthe microwave cavity. In a preferred embodiment, plasma to substratedistance is changed by moving the substrate holder 124 in a Z axis or upand down with respect to the antenna 106 which scans the plasma in anX-Y plane. Thus, the plasma to substrate distance can be closelycontrolled.

In accordance with techniques which are well-known, microprocessorcontroller 172 is preprogrammed to scan antenna 106, so as to move theplasma ball 144 to provide a uniform coating of diamond or othermaterial over the surface of substrate 142. The microprocessorcontroller 172 is also connected with computer driven stage 195 whichincludes actuator means for moving the substrate holder 124 in avertical direction with respect to the plasma as will be explained.Plasma to substrate distance thus can be optimized over the entiresurface of a substrate.

Sensor means are provided for optimizing the thickness of the diamondcoating or the like over the surface of the substrate 142 being coated.Such sensors, for example, are charge-coupled devices (CCDs), which havelow noise and are capable of high-resolution imaging. It is alsopossible to use any convenient means for scanning a locus of pointsdefining the surface of the substrate to be coated.

In a preferred embodiment, an optical based thin film sensor means 168is disposed for looking through the axis of antenna 106 as shown in FIG.2. The sensor means 168 is, for example, a charge-coupled device (CCD).The sensor means 168 provides high resolution imaging of the surface ofthe substrate 142 in accordance with techniques which are well known.The sensor means 168 is thus able to measure the thickness of thedeposited film over substrate 142 with extreme accuracy. Sensor means168 is adapted for producing output signals to microprocessor 172 overline 170. The output signals produced along line 170 to themicroprocessor 172 are representative of the precise thickness of thecoating to being applied to the substrate surface. The microprocessorthen uses these signals in a feedback control configuration, inaccordance with techniques which are well known to those skilled in theart, to automatically calculate the angle of inclination of the antenna106 and degree of upward or downward movement of the substrate holder124 for the locus of points which define the optimal contact between theplasma 144 and the substrate 142. This provides a coating of uniformthickness over the entire area of the substrate.

In a preferred embodiment, the microprocessor controller 172 analyzesthe incoming signals from the sensor 168 and produces a first set ofcontrol signals on output lead 174 to an actuator mechanism 176. Theactuator mechanism includes an arm 178 operatively connected to theantenna 106. A single spherical ball 182 and corresponding matingsurface 184 are disposed around the periphery of the antenna 106 at agiven point. The arm 178 of actuator mechanism 176 rotates the antenna106 about a desired axis of rotation in response to a first controlsignal from microprocessor controller 172. The axis of rotation of theantenna can be varied by changing the angle at which the antennaprojects into the process chamber through the spherical ball.

The antenna is swiveled about an axis of rotation defined by sphericalball 182. The angle of rotation also can be controllably selected sothat the antenna can be swiveled about a selectively larger or smallerarea.

The microprocessor produces a first set of signals along output leads tothe actuator mechanism 176 which are representative of the degree towhich the actuator mechanism 176 is to move the angle of inclination ofthe antenna 106 for each mapped point in the locus of points definingthe target surface of a given substrate. The antenna 106 is capable ofbeing swiveled about a pivot axis with at least two degrees of freedom.It will be appreciated that the antenna 106 can be rotated, swiveled andpivoted in order to make the plasma ball scan the entire surface of asubstrate.

In response to a second set of control signals from the microprocessor172, the substrate holder 124 moves the substrate 142 upward or downwardwith respect to the plasma. A second set of signals are sent by themicroprocessor over line 196 to computer driven stage 195. The signalsare representative of the degree to which the computer driven stage 195is to move the substrate holder 124 either downward or upward withrespect to each point in the locus of points which define the substratesurface in order to maintain a uniform coating over that surface.

The computer driven stage 195 includes an electrically actuable meansfor moving the substrate holder 124 in precise positional increments ina vertical direction with respect to antenna 106 in accordance withtechniques which are well known.

The foregoing features of the invention advantageously enable the plasmaball to be automatically directed in predetermined contact with a largersurface area of the target substrate than was previously possible. Inaddition, the foregoing features of the present invention enable theantenna to automatically direct the plasma ball to scan any type ofsurface at a predetermined uniform contact.

It will be appreciated that the present invention enables surfaces whichare non-uniform and nonplanar to be provided with a uniform coating of athin film diamond or other substance because the plasma ball isautomatically directed by the microprocessor controller and sensors tobe conformably directed to the target substrate surface and to maintaina uniform, predetermined distance from that surface. This enables aplasma CVD device according to the present invention to provide acoating of uniform thickness over any substrate surface. This provides agreat advantage over conventional plasma enhanced CVD devices which areincapable of coating a nonplanar substrate surface with a thin filmlayer having a uniform thickness.

A device according to the present invention is capable of optimizing theplasma to substrate distance over a greater area than was previouslypossible. In addition, the plasma to substrate distance is alsooptimized for nonplanar substrates. This achieves a much higher coatingrate for a thin film layer of uniform thickness than was previouslypossible. For example, in conventional ECR plasma enhanced CVD devices,a 2-6 inch wafer surface was about the largest surface capable of beingcoated with a thin film layer. However, the surface coating was by nomeans uniform. For example, a conventional ECR plasma CVD devicetypically provides a uniform coating over only 1 cm². In contrast, adevice according to the present invention is capable of coating a 4 inchwafer (approximately 75 cm²). Thus, the present invention is capable ofincreasing, by at least two orders of magnitude, the surface area of asubstrate which can be coated with a layer of uniform thickness using aplasma enhanced CVD process.

It should be noted that the present invention is not limited toproducing a diamond coating but can also be used for the deposition ofany thin film such as silicon oxide, silicon nitride, gallium nitride,or the like.

While the present invention can be used for any type of epitaxial orthin film coating, it has great advantages in the application of adiamond coating. In a conventional CVD device using an electroncyclotron resonance (ECR) plasma, a diamond deposition is approximatelyequal to the plasma diameter. Because the RF coupling antenna in aconventional microwave plasma CVD device is fixed or a capable ofvarying only the vertical elevation with respect to the plasma, coatingan area larger than the plasma diameter can be done only byrepositioning the substrate. However, in conventional microwave plasmaCVD devices, if the substrate holder or other substrate supporting meansare moved relative to an antenna with a fixed angular position, thestability of the resonant cavity formed in the process chamber 114 isdestroyed. This significantly limits the degree to which large areasubstrates can be uniformly coated using conventional plasma CVDdevices.

Thus, in accordance with the present invention for multiple passes ofthe plasma ball 144 over a target substrate, the resonant cavity of theprocess chamber can be maintained substantially constant. This has beenfound to greatly enhance the uniformity of the deposition process. Someconventional large area deposition systems (LADS) claim to be capable ofachieving twenty-five per cent uniformity of layer thickness over anarea eight inches in diameter. In contrast, using the process of thepresent invention, it has been found that a uniformly thick coating canbe achieved with variations of less than 10 percent.

Conventional feedback control methods enable the microprocessor 172 tokeep the plasma ball 144 accurately positioned on the substrate to forma uniform thin film coating. A series of positional intervals along asurface of the substrate holder are established by an encoding strip orother convenient means for indicating precise positional movement. In apreferred embodiment, these intervals are 0.100" of an inch apart butcould be any convenient distance. The intervals on the encoding stripcorrespond to precise positional intervals and are detected by aposition encoding means 192. The position encoding means 192 senses thedegree of rotation of the substrate holder 124. Position encoding means192 then produces output signals along line 194 to the microprocessorcontroller 172 which are representative of the degree of rotation of thesubstrate holder 124. The microprocessor controller 172 providesfeedback signals along line 174 to the actuator mechanism 176. Thesignals from the microprocessor along line 174 are representative of thedegree to which the actuator mechanism 176 is to move the angle ofinclination of the antenna 106 in order to maintain a uniform thin filmcoating on substrate 142, as the substrate holder 124 rotates.

The precise control achieved by the microprocessor controller 172 isaccomplished through conventional feedback control methods which arewell-known and can be implemented by one skilled in the art withoutundue experimentation.

In accordance with another embodiment of the invention as shown in FIG.5, a plurality of antennas are provided for controllably moving acorresponding plasma ignited at the transmitting end of each antenna, asdescribed with reference to FIGS. 1 and 2. This has the advantage ofcovering even large area substrates with a uniform coating of diamond,refractory materials, or the like.

Referring to FIG. 5, a process chamber 114, as described in detail withreference to FIGS. 1 and 2, is provided with a plurality of antennas106a, 106b, 106c, 106d, 106e. Each antenna 106a, 106b, 106c, 106d, 106e,is disposed for coupling microwave energy from a corresponding waveguide203a, 203b, 2032c, 203d, 203e.

Each antenna 106a, 106b, 106c, 106d, 106e is disposed in coaxialarrangement within a corresponding dielectric reflector means 202a,202b, 202c, 202d, 202e, respectively, as described above. The antennas106a, . . . 106e each have a transmitting end which terminates in acorresponding dielectric reflector 202a, . . . 202e within processchamber 114 as shown in FIGS. 1 and 2, as described previously.

The antennas 106a, . . . 106e are disposed substantially parallel to thedirection of the E field vectors in a corresponding waveguide 203a,203b, . . . 203e for producing maximized coupling efficiency of the Efields into the process chamber 114. Microwave energy is suppliedthrough a microwave generator 100, circulator 102 and rectangularwaveguide 104 including a stub tuner, as previously described withreference to FIGS. 1 and 2.

The plurality of antennas 106a, . . . 106e are also adapted to beswiveled about an axis of rotation with at least two degrees of freedomas described above. This optimizes contact between the substrate and aplurality of plasmas over a very large substrate area. The antennas areswiveled and moved with respect to the substrate in response to signalsfrom a microprocessor controller as shown in FIG. 2, in accordance withtechniques which are well known. As in the embodiment with a singleantenna, the invention is adapted for operation in open loop or closedloop mode. In an open loop mode, a sequence of plasma to substratecontact paths for the plasma associated with each corresponding antennais programmed into the microprocessor. The microprocessor then providescontrol signals to activate each antenna to direct the plasma in apredetermined contact with the substrate surface in accordance withknown techniques.

In a closed loop mode a substrate having an irregular or geometricallycomplex surface is scanned by a CCD imaging means or other convenientsensor means for producing output signals representative of surfacedeviations. The microprocessor, in accordance with well known adaptivefeedback techniques then activates selected antennas to move the plasmain an optimized contact path with the scanned portion of the substrateto provide the desired coating of diamond or refractory material.

It will be appreciated that the present invention provides a means foroptimizing the position of the plasma ball with respect to the locus ofpoints defining the surface of the substrate to be coated. Thus, thepresent invention provides an extremely reliable degree of repeatabilityfor stabilizing the plasma ball with respect to substrate surfaces whichare mapped in the microprocessor controller 172. The apparatus accordingto the present invention enables the plasma to be moved with a greaterdegree as to accuracy and repeatability over a wider area of thesubstrate than was previously possible with conventional methods. Thisadvantageously increases speed and uniformity of a plasma enhanced CVDprocess.

The invention is particularly well-suited to diamond deposition. Thesurface area of diamond deposition is approximately equal to the plasmadiameter. Accordingly, conventional methods which lack the presentcapability of swiveling the antenna in at least two degrees of freedomare seriously limited in the size of the substrate that can be coated.With conventional techniques, the substrate must be manuallyrepositioned in order to increase the area of the diamond coating.During the repositioning, the plasma must be turned off. This greatlyincreases the complexity and the time needed for a conventional plasmaenhanced CVD process.

In contrast, the present invention by pivoting the antenna about an axisof rotation in at least two degrees of freedom enables a diamond layerto be optimally coated over a much larger area with greater uniformitythan was previously possible. In addition, the present invention greatlyenhances the rate of diamond coating and the rate of other thin filmepitaxial coatings such as for gallium arsenide.

It will be appreciated that the foregoing aspects of the presentinvention provide the advantages of generating a high energy microwaveplasma with improved controllability for CVD processing. The presentinvention is capable of refractory material processing and is alsosuitable for chemical vapor infiltration. Thus, the present invention isalso adapted for forming ceramics for high temperature applications.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not limited to thedisclosed embodiment and alternatives as set forth above, but on thecontrary, is intended to cover various modifications and equivalentarrangements included within the spirit and scope of the appendedclaims.

What is claimed is:
 1. A plasma CVD apparatus suitable for forming alayer of material on a substrate comprising:a microwave generator meansfor generating microwave radiation; a waveguide means for guiding saidmicrowave radiation from said microwave generator; a process chamberincluding a means for receiving a reactant gas for forming a plasma andfurther including means for holding said substrate; coupling antennameans moveable about a axis of rotation with at least two degrees offreedom for coupling said microwave radiation from said waveguide intosaid process chamber and for controllably directing said plasma to alocus of positions defining an optimal plasma to substrate contact withrespect to said substrate to form a uniform layer of said materialthereon.
 2. An apparatus according to claim 1 wherein said processchamber further comprises:microprocessor means for mapping a locus ofpositions defining an optimal plasma to substrate contact over saidsurface of said substrate and for producing a first set of signals forrotating said coupling antenna with respect to an X-Y plane and forgenerating a second set of signals for moving the substrate holder withrespect to a vertical or Z axis; actuator means for rotating saidantenna in response to said first set of signals and for moving saidsubstrate holder in a vertical direction in response to said second setof signals from said microprocessor.
 3. An apparatus according to claim2 wherein said actuator means further comprises an electrically actuablepivot arm operatively connected with a rotatably driven disc forrotating said antenna in response to signals from said microprocessor.4. An apparatus according to claim 2 wherein said coupling antenna isinsertable into said process chamber through a spherical ball having abore for receiving said antenna, and said spherical ball being receivedin a corresponding mating member disposed in a wall of said processchamber to enable said coupling antenna to undergo angular rotation withat least two degrees of freedom with respect to said substrate.
 5. Anapparatus employing a microwave plasma for depositing a layer ofmaterial on a substrate comprising:a microwave source; a waveguide meansfor guiding microwaves from said microwave source; a process chamber formaintaining a constant resonant cavity including a base transparent tovisible and near infrared radiation, and means for supporting saidsubstrate over said base; coupling antenna means, swingably rotatableabout an axis or rotation and adapted for changing the angle ofrotation, for coupling said microwave radiation from said waveguide intosaid process chamber, to controllably direct a plasma ball in optimalcontact with said substrate; a lamp array disposed beneath said base ofsaid process chamber for heating said substrate through said transparentbase.
 6. An apparatus according to claim 5 wherein said base of saidprocess chamber comprises at least two layers of a material transparentto visible and near infrared radiation, said layers being separated byan interstitial space for receiving a circulating coolant.
 7. Anapparatus according to claim 6 further including pumping means forcirculating said coolant throughout said interstitial space.
 8. Anapparatus employing a microwave plasma for depositing a coating on thesurface of a substrate comprising:a microwave source for producingmicrowave radiation; a waveguide means for guiding said microwaveradiation and including means for impedance matching said microwaveradiation into a plasma load; a process chamber for providing a stableresonant cavity for formation of a plasma, said chamber having a topsurface, a base and enclosing side walls, wherein said base comprises amaterial transparent to visible and near infrared radiation and includesmeans for movably holding a substrate at a predetermined verticaldistance from said base; antenna means rotatable about a pivot axis forcoupling said microwave radiation into said process chamber; a lamparray means for heating said substrate through said transparent base toenhance formation of a nucleation layer on said substrate.
 9. Anapparatus according to claim 8 wherein said base further comprises atleast two plates separated by an interstitial space for receiving a flowof coolant such as water; andmeans for circulating said coolant betweensaid first and second plates to provide uniform cooling of said plates.10. In a plasma assisted CVD device employing a plasma for forming alayer of material on a substrate, said device including a microwavegenerator for generating microwave radiation, waveguide means forguiding said microwave radiation, a process chamber for holding asubstrate and for providing a stable resonant cavity for formation of aplasma, a coupling antenna means for coupling said microwave radiationfrom said waveguide into said process chamber; the improvementcomprising:means for rotating said coupling antenna about an axis ofrotation with at least two degrees of freedom for directing said plasmainto optimal contact with a surface of said substrate.
 11. An apparatusaccording to claim 10 wherein said means for rotating said couplingantenna includes a spherical ball and corresponding mating surfacedisposed in a wall of said process chamber, said spherical ballincluding a bore for receiving said antenna in slidable sealingengagement and for enabling rotation about a desired axis of rotation.12. An apparatus according to claim 11 wherein said means for rotatingsaid antenna with at least two degrees of freedom further includessensor means for detecting said layer of material deposited on saidsubstrate and for producing a series of output signals representative ofthe thickness of said layer;microprocessor means responsive to saidoutput signals from said sensor means for mapping a locus of positionsover said substrate surface to achieve optimal contact between saidplasma and said substrate and for producing output signalsrepresentative of said locus of positions; actuator means responsive tosaid output signals from said microprocessor for selectively rotatingsaid antenna about an axis of rotation and adapted to move saidsubstrate in a vertical position such that said antenna moves saidplasma to said locus of positions to form a substantially uniform layerof material over said substrate.
 13. An apparatus employing a microwaveplasma for depositing a layer of material on a substrate comprising:asource of microwave radiation; a waveguide means for guiding saidmicrowave radiation; a process chamber comprising an enclosure forproviding a stable resonant cavity for forming a microwave plasma,including substrate holder means adapted for rotation and for movementin a vertical axis for supporting said substrate; a coupling antennameans adapted to be pivoted about an axis of rotation for coupling saidmicrowave radiation from said waveguide into said process chamber andfor controllably moving said plasma over the substrate surface; actuatormeans for varying the pivot angle of said coupling antenna about saidaxis of rotation in response to control signals; microprocessor meansincluding a position encoding means for sensing the rotation of saidsubstrate holder and for producing output signals to said actuator meansfor varying the pivot angle of said coupling antenna about said axis ofrotation to maintain the resonant cavity at a constant state as saidsubstrate is rotated.
 14. An apparatus according to claim 13 furthercomprising means for moving said substrate holder up or down withrespect to said antenna in response to signals from said microprocessormeans.
 15. An apparatus employing a microwave plasma for depositing alayer of material such as diamond on a substrate comprising;a source ofmicrowave radiation; a waveguide means for guiding said microwaveradiation along a predetermined path and including means for impedancematching said microwave radiation with a plasma load; a process chambermeans for providing a stable resonant cavity for the formation of aplasma, including means for receiving a reactant gas and means forholding said substrate adapted for vertical movement; a coupling antennameans pivotally rotatable about a central axis for coupling saidmicrowave radiation from said waveguide means into said process chamberto form said plasma, and for directing the plasma to an optimal locus ofpositions for creating a uniform coating over the surface of thesubstrate.
 16. An apparatus according to claim 15 furthercomprising:means for imaging said substrate surface and for generatingoutput signals corresponding to a locus of positions representative ofthe optimal plasma to substrate contact for providing a uniform coatingof said material over said substrate; microprocessor means, responsiveto said output signals, for producing control signals such that theplasma is scanned to each position in said locus of positions on thesubstrate; actuator means including a rotatable, pivotally articulatedarm operatively connected with said coupling antenna for varying thepivot angle of said antenna in response to said control signals.
 17. Anapparatus according to claim 16 further comprising second actuatormeans, operatively connected with said means for holding said substrateand responsive to signals from said microprocessor means, for movingsaid substrate relative to said coupling antenna to achieve an optimalSubstrate to plasma contact for forming a uniform layer of said materialover said substrate.
 18. An apparatus as in claim 15 wherein saidcoupling antenna includes a centrally disposed longitudinally orientedbore for passing a coolant such as air.
 19. An apparatus for depositingdiamond and refractory materials on a substrate comprising:a source ofmicrowave radiation; a waveguide means for receiving said source ofmicrowave radiation; antenna means for coupling said source of microwaveradiation from said waveguide means into a process chamber for ignitinga stable plasma therein for treating said substrate; tuner meansoperatively connected with said waveguide means for oscillating the Efield component of said microwave radiation to produce an E field ofmaximized intensity at said antenna in said waveguide means; means forswiveling said antenna about an axis of rotation with at least twodegrees of freedom to thereby direct said plasma into desired contactsaid substrate.
 20. An apparatus according to claim 19 wherein saidantenna includes a first end for coupling an E field of maximumintensity within said waveguide means and a transmitting end fortransmitting said E field into said process chamber through a dielectricreflector.
 21. An apparatus for depositing diamond or a refractorymaterial, or the like on a substrate comprising:a source of microwaveradiation; a first waveguide means for concentrating said source ofmicrowave radiation to a maximum intensity; a plurality of outputwaveguide means operatively connected with said first waveguide meansfor directing said microwave radiation to a plurality of locations withrespect to a process chamber; a plurality of antenna means, each havinga first end disposed in a corresponding output waveguide means or forreceiving said maximized concentration of microwave energy therein and atransmitting end disposed in a portion of said process chamber fortransmitting said microwave radiation to ignite a respective plasma incontact with a substrate in said process chamber; rotary switch meansconnected between said plurality of output waveguide means and saidfirst waveguide means for switching said microwave energy from saidfirst waveguide means into said plurality of output waveguide means;such that a plurality of plasmas ignited at the transmitting end of eachcorresponding antenna are controllably directed to a correspondingportion of said substrate simultaneously.
 22. An apparatus fordepositing diamond or refractory materials or the like on a substratecomprising:a source of microwave radiation; a waveguide means forguiding said source of microwave radiation; a process chamber includinga substrate holder for holding said substrate therein; antenna meansrotatable about a pivot axis with at least 2 degrees of freedom forcoupling said microwave radiation from said waveguide means into saidprocess chamber to thereby controllably direct a plasma in desiredcontact with said substrate; tuner means disposed in said waveguidemeans for selectively oscillating an E field component of said microwaveradiation to provide an E field of maximum intensity for coupling intosaid antenna.
 23. An apparatus according to claim 22 wherein saidantenna comprises a radiating end disposed within a dielectric reflectormeans for minimizing losses in said microwave radiation as it is coupledinto said process chamber.